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    Circuit of a loop sensor based simple security alarm is described here. The sensor loop is nothing but a short length of thin enamelled copper wire, which bridges two input points of the electronic alarm circuit. When the loop is opened the alarm circuit fires an active electric/electronic hooter to raise an ear-splitting audio alert signal. The circuit requires 12 volt dc supply for proper working.

    When the loop is closed, anode terminal of diode D1 is at ground level and transistor T1 is off. When the loop opens, capacitor C1 is quickly charged via resistor R1 and diode D1, whereupon mosfet T1 comes on so that the hooter (BZ1) is switched on. If the loop is closed again, initial condition is maintained by grounding the anode of D1 and this stops the charging of C1. However, C1 is disharged fairly slowly via R2, so that T1 is not switched off immediately! This ensures that the alarm remains active for a little more time and then goes out slowly. This timeout can be changed by varying the value of R1,R2 and C1. Mosfet T1 may be one of many types of popular n-channel power mosfet, but it should be able to handle the selected 12V hooter of your choice.

    Wire break alarm circuit schematic

    wire break sensor alarm circuit schematic

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    33 Responses to "Wire Break Sensor Alarm"

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    1. it’s efficient if you provide circuit elements list and it’s applications

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    2. aliasgar poonawala says: on October 31, 2010 at 6:36 am

      sir it will be helpfull if u send me the applications,working principle,etc of this wire break sensor alarm project so that it will be helpful for me to make the project report,and give good presentation.please E-mail me the requires as soon as possible on “ALIASGAR_MIKAIL950@yahoo.com”
      i hope u will do the needful.

      ALIASGAR

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      • T.K.Hareendran says: on October 31, 2010 at 12:36 pm

        Working principle of this circuit is clearly described in the text portion of the article.Possible applications include luggage security system for travellers,burglar alarm unit for home/office protection,etc.

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      • Dear Sir

        In the text you say ‘C1 is disharged fairly slowly via R2′

        Should this be ‘through R2 and R3′?

        Thanks Bill

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    3. sir, can u please tell me how can i use trasformer in place of 12 v battery in this circuit

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    4. Use 12v trf to build a 12v dc powersupply ie battery eliminator.

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    5. is get the output

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    6. Rathod Anand M says: on March 28, 2011 at 9:08 am

      Sir, Pls which circuit i used to flow of pressure of water.
      Pls how can i used the pressure sensor for the measuring the water pressure.
      Please give me reply as soon as possible.

      Thank you

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    7. priya kala says: on March 29, 2011 at 2:16 pm

      sir it will be helpfull if u send me the applications,working principle,etc of this wire break sensor alarm project so that it will be helpful for me to make the project report,and give good presentation.please E-mail me the requires as soon as possible on

      Read more: http://electroschematics.com/6153/wire-break-sensor-alarm/#ixzz1HzD1YykV

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    8. sir …….can u plz send me the information why r3=100k is used.plz plz do reply sir

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    9. Dear Sir,
      I’ve replaced BUZ74 with IRF820,10uF/25V with 10uF/63V,1N4001 with 1N4007,as the mentioned parts are not available locally.But the circuit is not working.Please advice.

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    10. Arindam Roy says: on February 12, 2012 at 1:32 pm

      Dear Sir,
      I’ve replaced BUZ74 with IRF820,10uF/25V with 10uF/63V,1N4001 with 1N4007,as the mentioned parts are not available locally.But the circuit is not working.Please advice.

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    11. Hasir nisar says: on February 15, 2012 at 8:03 am

      Dear sir,
      what is the value of
      R2=4M7
      in this circuit?

      And one more question,

      what used of c2?
      C2′s + point connect to battery wire,
      and (-) point where connect?

      Pleas answer me………..
      HN..:)

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      • Arindam Ray says: on February 15, 2012 at 11:35 pm

        Hey Hasir nisar ! I have same problem as u faced,I simply grounded the C2′s – point,but end of all,the circuit is not working.you can see my previous query to the author about the changes/problems I faced.plz reply if u find some solution.

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      • R2 is 4.7 megohm. In the realm of resistance we measure in ohms, kilohms, and last but not least megohms.

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    12. Hasir nisar says: on February 21, 2012 at 6:27 am

      Hey,
      Arindam Ray,
      thanx for share your problem.
      I have circuit’s all same components are available
      but
      R2 confused me?:|
      > R2=4M7,
      what stand for “M”.
      Your New friend,
      HASIR NISAR. (DELHI)
      hasir_nisar@rediffmail.com

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    13. Hasir nisar says: on February 21, 2012 at 8:41 am

      Can i use
      TRANSFORMSLESS / TRANSFORM BASED POWER SUPPLY
      12v. 100mA
      for alarm circuit proper(24×7) work.
      Or
      # 12v. (how)?mA.
      HN….

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      • Arindam Ray says: on February 22, 2012 at 12:33 pm

        Hi, Hasir nisar

        Thanking You for your kind cooperation.

        I am facing some problem.

        As some components are not available in the
        Local market,I went for some compatible components
        Described by the author,but in fact the circuit is not
        Working at all.
        I’ve replaced BUZ74 with IRF820,10uF/25V with 10uF/63V,
        1N4001 with 1N4007,
        But the circuit is not working.
        Please advice.

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      • Hasir Nisar says: on February 27, 2012 at 9:02 am

        Hello,
        Arindam.
        I have an idea for you.
        Increase the battery power with
        15v. DC
        OR
        My question is pending
        r2=4M7
        meaning of ‘M’ ?
        HN..

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      • 4M7 = 4.7MΩ

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      • Hasir Nisar says: on February 27, 2012 at 4:54 pm

        In
        4.7R
        (Ohm denote by ‘R’)

        4.7K
        (Kilo Ohm denote by ‘K’)

        4.7M
        (What is denote by ‘M’)
        HN..

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      • Hasir Nisar says: on March 4, 2012 at 8:18 am

        Hey Arindam,
        your circuit works ?

        My circuit successful working but
        sound is LOW.
        What i do for high sound?
        YOU KNOW WHAT PROBLEM .

        Rply please. HN..

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    14. Alarm circuit that works?
      Sensor wire break after the alarm rings for how long?
      Please give your answer soon.

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    15. حاشير نيشار says: on March 5, 2012 at 8:52 am

      MY WIRE BREAK SENSORS ALARM CIRCUIT IS WORKING SUCCESSFUL .

      Very very very Thank you,
      ELECTRO SCHEMATIC
      P. MARIAN

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    16. jerry rani says: on March 13, 2012 at 4:43 am

      Sir,
      Can you please let me know what’s the purpose of the Capacitor C2??

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    17. Hello,
      P. Marian,
      you have same circuit in low current (3v/5v.)?

      What i do, the same circuit work in 3v.?
      I already made This circuit.

      SkyNet

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    18. BINDAAS,
      WEBSITE……….

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    19. Sir, Do you have any circuit that has unique sound which is suitable for car parking alarm? (Disregard fire alarm, police siren and any usual alarm.)

      Thank you Sir.

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    20. Dear Sir ,
      I have an requirement of detecting a sensor cable break alarm. we have a system that sense the powder. this sensor has a simple ss metal rod . there is two cable is connected to this sensor . one cable is connect to the ss rod and another cable is connected to the sensor shield the shield is normally ground. now when the powder is sense by sensor there will be some millivolts are genrated. that volts we measure .now when this two or one cable is break .so we get the alarm so please send me any circuit for this system if it is possible.

      thanks

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    21. Swapnil n. Rajput says: on June 19, 2012 at 11:01 am

      nice project . i like it

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    22. hello reader, i have problem in addressable fire alarm.
      i.e; 1, sounders open
      2, cable break
      3, device fault
      system name is premier quatro addressable fire alarm.
      i need solution. when u have plz revert me.

      thanks and warm regards
      aditya

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    23. priyanka ghule says: on April 7, 2014 at 7:13 pm

      sir can u pls send me the principle, aplication, and working of this ckt so it will help me in my project report.

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